fix(android_alarm_manager_plus): Fix integration test

[nohli]

Description

The integration test for the lower Android API level fails since it was recently changed from 21 to 22.

The test already failed in the PR changing the version, and since then in all workflow runs using the new API level. In a current PR, the test failed seven times in a row. Unless we find the actual cause, it makes sense to revert the API level change.

This PR changes the version to the one that worked fine before.

In the future, I would suggest only merging PRs with successful tests (if they worked before), so we limit regressions on main and fix the issue when it arises, which is easier than finding the cause afterwards and having issues in unrelated PRs.

This change was already included in #2112 to check if it helps. Suggestion is to first merge this one, rebase, and merge the other one.

Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I titled the PR using Conventional Commits.
• I did not modify the CHANGELOG.md nor the plugin version in pubspec.yaml files.
• All existing and new tests are passing.
• The analyzer (flutter analyze) does not report any problems on my PR.

Breaking Change

Does your PR require plugin users to manually update their apps to accommodate your change?

• Yes, this is a breaking change (please indicate that with a ! in the title as explained in Conventional Commits).
• No, this is not a breaking change.